This application is related to the co-filed and commonly assigned applications, attorney docket number 303.478us1, entitled xe2x80x9cCircuits and Methods for Body Contacted and Backgated Transistors,xe2x80x9d and attorney docket number 303.498us1, entitled xe2x80x9cAnother Technique for Gated Lateral Bipolar Transistorsxe2x80x9d which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to semiconductor integrated circuits. More particularly, it pertains to circuits and methods for dual-gated transistors.
2. Background of the Invention
Integrated circuit technology relies on transistors to formulate vast arrays of functional circuits. The complexity of these circuits requires the use of an ever increasing number of linked transistors. As the number of transistors required increases, the surface area that can be dedicated to a single transistor dwindles. It is desirable then, to construct transistors which occupy less surface area on the silicon chip/die.
Integrated circuit technology uses transistors conjunctively with Boolean algebra to create a myriad of functional digital circuits, also referred to as logic circuits. In a typical arrangement, transistors are combined to switch or alternate an output voltage between just two significant voltage levels, labeled logic 0 and logic 1. Most logic systems use positive logic, in which logic 0 is represented by zero volts, or a low voltage, e.g., below 0.5 V; and logic 1 is represented by a higher voltage.
One method in which these results are achieved involves Complementary Metal-Oxide Semiconductor (CMOS) technology. CMOS technology comprises a combination of oppositely doped Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETs) to achieve the switching mechanism between voltage levels associated with logic 0 and that of logic 1. This configuration is likewise referred to as an inverter. Conventional CMOS inverters consume an appreciable amount of chip surface area, even despite ongoing reductions in the critical dimensions that are achievable with conventional photolithography techniques. The critical dimension (F) represents the minimum lithographic feature size that is imposed by lithographic processes used during fabrication. It is one objective, then, to fabricate CMOS inverters which conserve silicon chip surface space.
Standby current is another significant concern and problem in low voltage and low power battery operated CMOS circuits and systems. High threshold voltage transistors and high power supply voltages were traditionally employed in part to minimize subthreshold leakage at standby. Today, however, low voltages are desired for low power operation. This creates a problem with threshold voltages and standby leakage current. In order to get significant overdrive and reasonable switching speeds the threshold voltage (Vt magnitudes must be small, e.g. zero volts. However, having such low threshold voltages generally-causes one of the transistors to have a large subthreshold leakage current. Various techniques have been employed to allow low voltage operation with CMOS transistors and to maintain low subthreshold leakage currents at standby. Dynamic CMOS circuits achieve this objective by using clock or phase voltages to turn off conduction from the power supply to ground through the chain of devices when the inverter is at standby. Synchronous body bias has similarly been employed in part to minimize subthreshold leakage. However, synchronous body bias, like dynamic logic, requires extra clock or phase voltage lines throughout the circuit. This increases considerably the complexity of circuits and consumes precious space on the chip. Also, data stored only on a dynamic basis must be clocked and refreshed.
Another way to get around these problems involves implementing resistors to provide a source to substrate bias or backgate bias when the transistor is in the off state. This reverse bias is also termed a xe2x80x9cswitched source impedance.xe2x80x9d The resistor technique is effective for reducing subthreshold leakage current at standby. However, the problem with this method is that resistors are troublesome to fabricate in CMOS process steps.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need for improved inverter devices. The improved inverters should desirably minimize subthreshold leakage current and conserve chip surface space while continuing to advance the operation speeds in logic circuits. The improved inverter circuits and structures should remain fully integral with CMOS processing techniques.
The above mentioned problems with memory devices and other problems are addressed by the present invention and will be understood by reading and studying the following specification. A circuit and method is provided to minimize subthreshold leakage currents at standby in low power CMOS circuits and systems.
In particular, an illustrative embodiment of the present invention includes an inverter. The inverter includes a first, second, third and fourth transistor which all extend outwardly from a semiconductor substrate. The transistors each have an upper surface and opposing sidewall surfaces. The transistors each have a source/emitter region, a body/base region, a collector/drain region, a first gate on a first one of the opposing sidewall surfaces, and a second gate on a second one of the opposing sidewall surfaces. There is an electrical contact between the collector/drain regions of the second and third transistors to provide an output for the inverter. A gate contact interconnects the transistors wherein the gate contact provides an input to the inverter.
In another embodiment, an inverter array is provided. The inverter array includes multiple inverters formed in an array. Each inverter includes the structure disclosed above. A metallization layer selectively interconnects the inputs and outputs of the inverters to form a logic circuit that accepts inputs and produces one or more logical outputs.
In another embodiment, an input/output device is provided. The input/output device includes a functional circuit which has a plurality of components. A logic device couples to the functional circuit. The logic device has a number of inverters formed in an array. Each inverter includes the structure disclosed above. The logic device includes a metallization layer that selectively interconnects the inputs and outputs of the inverters to form a logic circuit that accepts inputs and produces one or more logical outputs.
In another embodiment, a method of fabricating an inverter is provided. The method includes forming a first, second, third and fourth transistor. Each transistor extends outwardly from a semiconductor substrate. The transistors are each formed to have an upper surface and opposing sidewall surfaces. Each transistor is formed with a source/emitter region, a body/base region, a collector/drain region, a first gate formed on a first one of the opposing sidewall surfaces, and a second gate formed on a second one of the opposing sidewall surfaces. The method further includes forming an electrical contact between collector/drain regions of the second and third transistors to provide an output for the inverter. A gate contact is formed that interconnects the transistors and provides an input to the inverter.
In another embodiment, an inverter circuit is provided. The inverter circuit includes a complementary pair of transistors. The complementary pair includes a first channel type transistor and a second channel type transistor. Each transistor includes a body region formed of single crystalline semiconductor material and that extends outwardly from a substrate. The body region has an upper surface and opposing sidewalls. A source/emitter region is formed within a portion of the upper surface of the body region. A collector/drain region is formed within a portion of the upper surface of the body region. A first gate is formed on a first one of the opposing sidewalls. A second gate is formed on a second one of the opposing sidewalls. There is an electrical contact between collector/drain regions of the complementary pair to provide an output for the inverter. A gate contact interconnects the first gates of the complementary pair and serves as an input to the inverter.
In another embodiment, a method of fabricating an inverter is provided. The method includes forming a complementary pair of transistors. The complementary pair includes a first channel type transistor and a second channel type transistor. Forming each transistor includes forming a body region formed of single crystalline semiconductor material which extends outwardly from a substrate. The body region has an upper surface and opposing sidewalls. A source/emitter region is formed within a portion of the upper surface of the body region. A collector/drain region is formed within a portion of the upper surface of the body region. A first gate is formed on a first one of the opposing sidewalls. A second gate is formed on a second one of the opposing sidewalls. The method further includes forming an electrical contact between collector/drain regions of the complementary pair to provide an output for the inverter. The method also includes forming a gate contact to interconnect the first gates of the complementary pair and serve as an input to the inverter.
In another embodiment, an information handling system is provided. The information handling system includes a central processing unit, a random access memory, and a system bus. The system bus communicatively couples the central processing unit to the random access memory. The central processing unit (CPU) further includes an inverter which has the structure describe above.
Thus, improved inverter structures are provided along with circuits and methods for the same. These new inverter structures provide for low voltage operation and enhanced switching action over conventional complementary metal-oxide semiconductor (CMOS) devices. These improved inverter structures significantly reduce standby leakage current in low power operation devices. Forming the inverter structures is fully compatible with CMOS processing technology. The inverter structures additionally conserve precious chip surface space.
These and other embodiments, aspects, advantages, and features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art by reference to the following description of the invention and referenced drawings or by practice of the invention. The aspects, advantages, and features of the invention are realized and attained by means of the instrumentalities, procedures, and combinations particularly pointed out in the appended claims.